1. Technical Field
The present disclosure generally relates to a surgical apparatus for fusing adjacent bone structures, and, more particularly, to an apparatus and associated method for fusing adjacent vertebrae.
2. Background of the Related Art
The fusion of adjacent bone structures is commonly performed to provide for long-term replacement to compensate for degenerative or deteriorated disorders in bone. For example, an intervertebral disc, which is a ligamentous cushion disposed between adjacent vertebrae, may undergo deterioration as a result of injury, disease, tumor or other disorders. The disk shrinks or flattens leading to mechanical instability and painful disc translocations.
Conventional procedure for disc surgery include partial or total excision of the injured disc portion, e.g., discectomy, and replacement of the excised disc with biologically acceptable plugs or bone wedges. The plugs are driven between adjacent vertebrae to maintain normal intervertebral spacing and to achieve, over a period of time, bony fusion with the plug and opposed vertebrae. More recently, emphasis has been placed on fusing bone structures (i.e., adjoining vertebrae) with metallic or ceramic prosthetic cage implants. One fusion cage implant is disclosed in commonly assigned U.S. Pat. No. 5,026,373 to Ray et al., the contents of which are incorporated herein by reference. The Ray ""373 fusion cage includes a cylindrical cage body having a thread formed as part of its external surface and apertures extending through its wall which communicate with an internal cavity of the cage body. The fusion cage is inserted within a tapped bore or channel formed in the intervertebral space thereby stabilizing the vertebrae and maintaining a pre-defined intervertebral space. Preferably, a pair of fusion cages are implanted within the intervertebral space. The adjacent vertebral bone structures communicate through the apertures and with bone growth inducing substances which are within the internal cavity to unite and eventually form a solid fusion of the adjacent vertebrae. FIGS. 1-2 illustrate the insertion of a pair of the Ray ""373 fusion cages positioned within an intervertebral space.
Accordingly, the present invention is directed to further improvements in spinal fusion procedures. In accordance with a preferred embodiment, an apparatus for facilitating fusion of adjacent bony structures includes an implant body dimensioned for positioning between adjacent bone structures to maintain the bone structures in desired spaced relation during interbody fusion. The implant body has an outer wall and an external threaded configuration disposed on the outer wall. At least one concave surface at least partially extends along the implant body. The concave surface advantageously reduces the transverse cross-sectional dimension of the implant member thereby facilitating placement of the implant member in restricted intervertebral areas. In addition, the concave surface enables placement of a pair of implants in nested side-by-side relation. Preferably, the threaded configuration has portions removed along an arc section of the outer wall thereby defining a series of generally longitudinally aligned concave surfaces in individual turns thereof. A system and method for facilitating fusion of adjacent vertebrae is also disclosed.